1. Field of the Invention
The present invention relates to a pneumatic radial tire which is excellent in a durability of a bead portion.
2. Description of the Related Art
Conventionally, in a pneumatic radial tire, particularly in a tire which is used in a heavy vehicle such as an industrial vehicle, a construction vehicle or the like, there is fear that a failure such as a separation or the like is brought about while beginning at a turn-up end of a carcass ply which is turned up around a bead core, and provision of a chafer is generally carried out for improving a durability of a bead portion. The chafer is arranged in such a manner as to enwrap the carcass ply from an inner side in a tire width direction to an outer side, around the bead core (refer, for example, to JP-A-07-164838 and JP-A-11-1107).
In the meantime, in the bead portion, it is known that a shear deformation in a tire circumferential direction is dominant in the inner side in the tire width direction, and on the other hand, a compression deformation in a tire radial direction is dominant in the outer side in the tire width direction. Accordingly, it is possible to improve the durability of the bead portion by effectively carrying out reinforcement against the deformations by the chafer.
In JP-A-07-164838, since an angle of inclination of a steel cord with respect to the tire radial direction of the chafer comes to 0 to 10 degrees in any chafer end portions in the inner side and the outer side in the tire width direction, the reinforcing effect against the shear deformation in the tire circumferential direction is not sufficient particularly in the inner side in the tire width direction.
Further, JP-A-11-1107 is structured such that an angle of inclination of an outermost terminal end portion in the tire radial direction in each of the outer side and the inner side of the tire is in a range between 22 and 35 degrees, and an angle of inclination at a position in each of the outer side and the inner side of the tire in the vicinity of a straight line which is parallel to a tire rotating axis passing through a center of gravity of a cross sectional figure of the bead core has an angle obtained by adding an angle within a range between 5 and 50 degrees to the angle of inclination of the outermost terminal end portion, with regard to the angle of inclination with respect to the tire circumferential direction of the steel cord in the bead reinforcing layer (corresponding to the chafer). According to this structure, it is possible to carry out reinforcement at a certain degree against the deformation in any of the inner side and the outer side in the tire width direction, around the bead core.
However, in the steel cord of the chafer of JP-A-11-1107, since the angle is rapidly changed between the vicinity of the outermost terminal end portion in the tire radial direction, and the vicinity of the straight line which is parallel to the tire rotating axis passing through the center of gravity of the cross sectional figure of the bead core, there has been a fear that a rigidity step is generated in the portion so as to cause a failure.